The present invention relates generally to deep water offshore drilling operations which utilize floating rigs, and more particularly, to a method for installing a drilling assembly, including a drive pipe, into a sea-bottom formation.
In deep water drilling operations, shallow water flow (SWFT) hazards have become increasingly troublesome. SWF derives its name from the phenomena of a flow, emanating from a subsurface and overpressurized zone, back to the seafloor. An overpressurized subsurface zone is formned naturally when an impermeable seal is formed over sandy settlements by rapid deposition of silty material. As the silty material is deposited over the sealed, sandy aquifer, the trapped water in the sandy settlement is unable to escape. Over time, the pressure increases in the sandy aquifer until the pressure developed is equal to or greater than the hydrostatic pressure at the depth of water at the location of the sandy aquifer. A shallow water flow occurs when the impermeable seal of silty material is penetrated to release the overpressure within the sandy aquifer. In some cases, the pressures are high enough to cause powerful flows of water and sand into the well bore. Waterflows destabilize the wellbore through erosion to collapse and in some cases damage the well bore and others adjacent thereto. Shallow waterflow hazards have been encountered in many areas of the world and continue to be a problem in deepwater drilling operations.
One solution for avoiding shallow waterflow hazards is to use a drive pipe. The drive pipe is driven into the formation past the high pressure sandy aquifer. The purpose of the drive pipe is to prevent the formation from collapsing into the borehole during this initial drilling. Since the drive pipe is driven into the formation, the soil is compressed and compacted in the immediate vicinity of the drive pipe. Compacted soil seals the drive pipe in the formation to prevent shallow water flow around the drive pipe. The drive pipe becomes the casing for the well bore through which subsequent drilling operations may be conducted.
In a typical offshore drilling installation, a length of drive pipe is hung from the floating rig by a string of drill collars and drill pipe lowered to the sea bottom. In such a deepwater installation, the water depth may be up to 10,000 feet or greater. In the drilling assembly, the string of drill collars are connected to the top of the drive pipe by way of a running tool having a J-latch, or other releasing mechanism. The drilling assembly may also be connected to the drive pipe by way of a conventional J-latch assembly engaged with lugs or other means attached to the inside or outside of the drive pipe. The drill string continues below the running tool and extends down the entire length of the interior of the drive pipe. The lower end of the drill string assembly terminates with a jet sub or downhole motor connected to a stabilized drill bit.
In a conventional assembly, the drill bit is located at the mouth or lower opening of the drive pipe, and is driven by the motor to function as a jetting assembly to drill a hole approximately the size of the inner diameter of the drive pipe. The drill string is initially connected to the drive pipe through a first position of the running tool to enable both elements to move downwardly together. Therefore, as the drill bit penetrates the sea bottom formation, the drill string lowers, and the drive pipe falls snugly into the bore hole made from the rotating and jetting action of the bit. This drilling continues until substantially the entire section of drive pipe penetrates the formation or until such time as the gravitational forces acting on the drive pipe will no longer overcome the effect of skin friction. Once this is accomplished, the drill string is disconnected from the drive pipe at the running tool connection to enable the drill string to move independently with respect to the drive pipe, and continue its drilling operation. In this mode, the drill bit continues to drill beyond the drive pipe, into the formation, while the drive pipe remains stationary.
During the initial drilling, when the drive pipe is penetrating into the formation due to gravitational force, regular seawater is utilized as the drilling fluid. Thus the sea water, traveling down through the interior of the drill string, functions to clean the bore hole bottom, and carry the cuttings up the annulus formed by the exterior of the drill string and the interior of the drive pipe. This fluid then exits the annulus at the top of the drive pipe to be released into the sea.
For subsequent drilling, the drill string is pulled out of the hole and the drill collars are stood back on the derrick of the floating platform. A conductor pipe is lowered from the rig to extend and attach to the top of the drive pipe to communicate with the annulus inside the drive pipe. Regular drilling mud is then utilized in the drilling operation by having it pumped down the drill string and up through the annuluses of the drive pipe and the conductor pipe. This conductor pipe also serves as a means to bring cuttings from the drill bit to the surface.
Drive pipes are usually 30 to 36 inches in diameter, having a wall one inch thick, although in some instances, the drive pipe can be 42 inches, or larger, in diameter, with a two inch wall thickness. Drive pipes are typically 350 to 450 feet in length for shallow water drilling operations if driven from the surface. In conventional drilling operations, it has been found that a drive pipe can not penetrate beyond a certain amount, usually around the 450 feet length, because at that length, the resistance caused by skin friction becomes greater than the force of gravity and the force applied from the surface by conventional hammer means. The drive pipe will reach a point of refusal and any further force applied to the uppermost section of the drive pipe will cause yielding of the pipe material and any further driving efforts must be discontinued.
In deep water drilling operations, drive pipes having lengths of 1000 feet or more are sometimes required to mitigate shallow water flow hazards. Therefore, auxiliary means for driving drive pipes are necessary to augment the gravitational forces acting on the drive pipes to increase the depth of penetration of the drive pipes.
One option has been to use a hammer applied to the top of the drill string to help drive the drive pipe at the end of the drill string downward. However, because of the great drill string lengths involved, the energy transferred to the drive pipe through the drill string is not sufficient.
A further option has been to apply conventional hammers directly to the top of the drive pipe at the connection between the drive pipe and the drill sting. Hydraulic pile and pipe drivers of various configurations are known. An example of a hydraulic pipe driver attached to the top of the pipe is disclosed in U.S. Pat. No. 4,964,473, incorporated herein by reference. The device has a submerged power converter wherein hydraulic pressure energy is generated in the power converter to drive the driver and wherein the power converter is driven by pressurized surrounding water after the energy transfer is exhausted into the surrounding water. Further examples of pipe drivers used to drive pipes and piles into a sea bed for securing platforms and other structures are disclosed in U.S. Pat. No. 4,601,349; 5,662,175; 5,090,485; 4,817,734; 4,818,149; 4,856,938; 5,088,567; 4,872,514; and 5,228,806, all incorporated herein by reference.
In any drive system using a conventional hydraulic hammer applied to the top of the drive pipe, there are significant drawbacks: (1) an umbilical conduit must be run from the floating vessel to the hammer; (2) conventional hydraulic hammers apply relatively low impacts; and (3) the drive pipe is not driven vertically. First, typical drive pipe hammers have umbilical cables which supply electrical or hydraulic forces to the hammers. At water depths where drive pipes are required (5,000-7,000 feet), the umbilical cord required is an impractical length. Second, conventional hydraulic hammers do not deliver large enough impacts to drive the drive pipe. Since the impact is delivered to the top of the drive pipe, the relative small impact energy is absorbed by the lengthy drive pipe. Impacts applied directly to the drive pipe may damage the pipe. Third, the drive pipe is not always driven straight down, as desired. Instead, the drive pipe more than likely deviates from vertical as it is driven. An installed drive pipe, which is not vertical, is generally unacceptable for subsequent drilling operations.
Conventional hammers are made even less effective by the need to use a xe2x80x9cconexe2x80x9d shaped driving shoe to penetrate the formation. Since the conventional hammers must be attached to the top of the drive pipe, there is no ability to run a mud motor/drill device into the drive pipe from the drill string. Therefore, a driving shoe must be placed at the leading end of the drive pipe to compress and deviated the soil from locations immediately beneath the drive pipe to locations around the drive pipe. This increases the skin friction on the outside of the drive pipe which further impedes the drive pipe""s progress into the formation. Similarly, if a conventional hydraulic hammer on an umbilical conduit is positioned within the drive pipe to impact the drive pipe at a point towards its bottom, a driving shoe must be employed. If the hydraulic hammer is within the drive pipe, it is impossible to dispose of the formation xe2x80x9ccorexe2x80x9d as the pipe is being driven. Thus, it is impossible to place a conventional hammer within the drive pipe.
Therefore, there is a need for a drive pipe driving system which does not require an umbilical conduit, applies a sufficient impact to drive the drive pipe, and drives the drive pipe vertically. The drive system must also be versatile to allow for a drive pipe having a driving shoe or a drill located in the mouth of the drive pipe.
The present invention obviates the above-mentioned problems by providing impact forces from within the drive pipe at a location toward the bottom or leading end of the drive pipe. In this manner, the energy transfer is much more efficient, and the pipe will be driven vertically.
The drilling assembly includes an impact tool hung, under tension, to the drill string directly below the running tool connection. An isolator is installed into the drill string directly above the running tool connection to prevent shock loads from being transferred to the drill string above.
The impact tool comprises inner and outer tubular body members, relatively movable with respect to each other, in an axial direction. The inner body member is connected to the upper drill string extending to the rig. The outer body member is connected to the lower drill string section that extends within the drive pipe to the drill bit. In this embodiment, the inner body member remains stationary, while the outer body member is movable in the up and down direction.
The impact tool further comprises a jar section for providing a downward jarring force on the inner body member which, in turn, transfers the jarring force to the top of the drive pipe through the running tool assembly. The tool also comprises one or more pull sections for providing a closing force between the two members to lift the outer member, the lower drill string, and the drill bit off the bore hole bottom. The jarring force is caused by releasing the last mentioned three components and allowing them to drop a predetermined distance, at which time impact occurs within the body of the jar. The impact tool further comprises a compression chamber or a mechanical device such as a spring, to function as an energy intensifier to augment the jarring force acting on the drive pipe.
The isolator includes two members axially movable with respect to each other, and interconnected to adjacent upper and lower drill collar sections. The isolator includes a compression chamber formed between the two members. The isolator functions to enable the drill string located above the running tool to elongate in order to compensate for the sudden travel of the drive pipe as it is being jarred downwardly. This enables the drill collars above the running tool assembly to remain in tension during operation to prevent unwanted vertical deviation of the drive pipe during installation.
Finally, a compensating tool is located on the drill string adjacent the motor and the bit. This tool also includes two members axially movable with respect to each other for connection to adjacent upper and lower drill collar sections. The compensating tool also includes a compression chamber formed between the two members. The tool functions to enable the drill string located adjacent the drill bit to become shorter to compensate for the sudden travel of the drive pipe downwardly and prevent the bit from impacting heavily on the formation. The compensating tool allows some slack in the string to allow the bit to rise and therefore prevent the bit from plugging while the drive pipe is being jarred into the formation. The drill bit and downhole motor drill out the formation xe2x80x9ccorexe2x80x9d, if so desired.
Other advantages of the inventive system are the ability to infinitely vary the impact loads, alter the location of the impact within the length of the drive pipe and the equal distribution of a large uniform mass, all of which contribute to the desirability and performance of the tool. Overall, the assemblies and methods of the present invention perform better than conventional hydraulic hammers.
A system for floating rig installations is provided for efficiently driving an extraordinarily long length of drive pipe into the sea bottom formation, while still preserving the integrity of the rig and the bottom hole assembly.
With the system of the present invention, the drive pipe is driven into the subsea formation with the drill string above the drive pipe in constant tension. A reciprocation occurs within the drive pipe so that the drive pipe may be driven from a floating vessel. The entire weight of the drive pipe and impacting system is suspended on a compressed gas within a cylinder of an isolation sub. The isolation sub prevents shock loads from being transferred up the drill string to the floating vessel.
In one embodiment of the invention, pump pressure lifts the bottom hole assembly and closure jar. Thus, pump pressure is ultimately transformed into an impact force on the drive pipe when the lifted mass is allowed to free fall onto the drive pipe. Lift pistons within the impact tool are designed to move out of the way when a pressure differential across them changes. This insures that the lift pistons do not impede the falling velocity of the mass prior to impact. Depending on the particular system, welded or preformed lugs are positioned inside the drive pipe to transfer impact loads from the impact tool to the drive pipe. Some systems of the present invention have an isolator, an impact device and a cushion sub used in combination.
While some embodiments of the invention simply allow the mass (drill collars) to freefall, in other embodiments a device is used to enhance or amplify the downward acceleration of the mass. For example, released potential energy stored in a spring, compressed gas chamber, combustion chamber, etc. is used to accelerate the falling mass in addition to gravity.
Many systems of the invention use a vertically reciprocating weight suspended within the drive pipe, but attached to the top and bottom of the drive pipe. Thus, the impact tool is used in conjunction with the relatively stationary running tool. The running tool may be latched or unlatched from the drill string. Thus, if the drilling motor stalls, the running tool may be unlatched from the drill string so that the drilling motor may be lifted up relative to the formation core to free the drill bit. In alternative embodiments, gas or pump pressure is used to cushion the drill bit from impact forces on the drive pipe. If the drill-out system is used, the ability of the motor and drill bit to float on top of the formation and not impact the bottom is a key feature.
In alternative embodiments, the inner members of the impact device are held stationary relative to the drive pipe during impact. Of course, since the drive pipe is driven into a subsea formation, the impact tool is used underwater in most systems of the present invention.
One aspect of the present invention is to use a detent to suspend the mass (drill collars) momentarily to provide the lift cylinders enough time to decompress. In one embodiment, the detent is a cylinder with a detent ring. Belleville springs cushion the detent cylinder when the drill collars are at the end of the raising stroke. Depending on the time delay necessary for suspending the mass, the detent ring will be either a short cocking detent or a long cocking detent. An example of a xe2x80x9cshort cockedxe2x80x9d detent is disclosed in U.S. Pat. No. 5,174,393, incorporated herein by reference.
While the present invention is described for use in driving a drive pipe into a subsea formation, the system could also be used to set subsea anchors or any other device which must be driven into a subsea formation.
Within the impact device, there are hydraulic tattle-tales to determine open and closed positions of the tool. While any type of tattle-tale known to persons of skill may be used, one particular type comprises a rubber sleeve containing grease or oil. A pressure sensor detects the pressure of the grease or oil within the rubber sleeve. This information is returned to the operator at the surface.
According to one aspect of the invention, there is provided a method for driving a drive pipe into a subsea formation, the method having the steps of: accelerating at least one mass relative to the drive pipe, wherein the at least one mass is accelerated within the drive pipe; and transferring energy from the accelerated at least one mass to the drive pipe.
According to a further aspect of the invention, there is provided a method for driving a drive pipe into a subsea formation, the method being comprised of the following steps: suspending the drive pipe from a drill string; moving at least one mass in a direction having an upward component and within the drive pipe; accelerating at least one mass relative to the drive pipe, wherein the at least one mass is accelerated within the drive pipe; transferring energy from the accelerated at least one mass to the drive pipe; isolating the drill string from energy from the accelerated at least one mass; and removing a core of formation from within the drive pipe after the transferring.
According to still another aspect of the invention, there is provided a method for driving a drive pipe into a subsea formation, the method having the following steps: suspending the drive pipe from a drill string; removably attaching the drill string to the top of the drive pipe; moving at least one mass in a direction having an upward component and within the drive pipe; accelerating at least one mass relative to the drive pipe, wherein the at least one mass is accelerated within the drive pipe; transferring energy from the accelerated at least one mass to the drive pipe near a bottom of the drive pipe; and isolating the drill string from energy from the accelerated at least one mass.
Relative to another aspect of the invention, there is an impact tool for driving a drive pipe into a subsea formation, the impact tool having: at least one mass adapted to fit within the drive pipe; an accelerator of the at least one mass; and a transferror of energy from the at least one mass to the drive pipe, wherein the transferror transfers energy after the at least one mass is accelerated by the accelerator.
In a further aspect of the invention, there is provided a system for driving a drive pipe into a subsea formation, the system having: a drill string suspendable from a marine vessel; a running tool attachable to the drill string, wherein a top of the drive pipe is connected to the running tool; at least one mass adapted to fit within the drive pipe; an accelerator of the at least one mass, wherein the accelerator is in mechanical communication with the running tool and the at least one mass; and a transferror of energy from the at least one mass to the drive pipe, wherein the transferror transfers energy after the at least one mass is accelerated by the accelerator.
In an alternative aspect of the invention, there is a system for driving a drive pipe into a subsea formation, the system having: a drill string suspendable from a marine vessel; a running tool attachable to the drill string, wherein a top of the drive pipe is connected to the running tool; an isolator sub between and in mechanical communication with the drill string and the running tool; at least one mass adapted to fit within the drive pipe; an accelerator of the at least one mass having: a first body member mechanically communicable with the at least one mass, a second body member mechanically communicable with the running tool, an actuator of the first and second body members relative to each other, wherein the actuator works against gravity, and a detent of the first and second body members relative to each other; the system further having an impulse section that accelerates the at least one mass; and a transferror of energy from the at least one mass to the drive pipe, wherein the transferror transfers energy after the at least one mass is accelerated by the accelerator.